Genetics: Mendel's Laws of Inheritance

• Genetics and Evolution are the main topics in Unit VII.
• This unit examines and explains the structure, function of DNA, story, and theory of evolution.

Genetics

• Genetics addresses questions about heredity by seeking to understand how an elephant always gives birth to baby elephant and not other animal, why mango seeds only grow into mango tress, why some siblings look similar and others do not
• Genetics deals with inheritance and variation of traits from parents to offspring.
• Inheritance is how traits pass from parent to offspring and forms the basis of heredity.
• Variation is the degree to which offspring differ from their parents.
• Humans understood that sexual reproduction hid causes of variation as early as 8000-1000 B.C
• People used the variations of wild plants and animals to selectively breed organisms with desirable traits.

Mendel's Laws of Inheritance

• Gregor Mendel's hybridization experiments with garden peas (1856-1863) led to laws of inheritance.
• Mendel applied statistical analysis and mathematical logic to biology, collected data from large samples, and confirmed inferences from test plants through successive generations, proving his results pointed to substantiated general rules rather than unsubstantiated ideas.
• Mendel studied contrasting traits such as tall/dwarf plants and yellow/green seeds, allowing him to create the rules governing inheritance
• Mendel used true-Breeding pea lines for artificial pollination/cross-pollination experiments, resulting in stable trait inheritance and expression.
• Mendel chose 14 true-breeding pea plant varieties.

Contrasting Traits Studied by Mendel

• Stem Height: Tall/dwarf
• Flower color: Violet/white
• Flower position: Axial/terminal
• Pod shape: Inflated/constricted
• Pod color: Green/yellow
• Seed shape: Round/wrinkled
• Seed color: Yellow/green

Inheritance of One Gene

• Mendel crossed tall and dwarf pea plants, collecting seeds and growing them into the first hybrid generation.
• Filial(offspring) or F1 , was all tall plants
• He found that the F1 always resembled one parent, with no sign of the trait from the other parent, so when tall was crossed with green, all offspring were tall
• Mendel self-pollinated the tall F1 plants and found that some of the offspring in the Filial2, generation were dwarf.
• 1/4 of the F2 plants were dwarf, while 3/4 were tall, showing no blending.
• Only one of the parental traits was expressed in the F1 generation, but both traits showed at the F2 stage at 3:1.

Factors & Genes

• Mendel proposed that something was being passed down through gametes which he called factors, now known as genes
• Genes contain the information needed to express a particular trait and the units of inheritance.
• Alleles are genes coding for a pair of contrasting traits.
• Uppercase letters represent traits expressed at the F1 stage, while lowercase letters represent the other trait, such as T for Tall and t for dwarf.

Genotypes & Phenotypes

• TT and tt are homozygous, while TT and tt are the genotype and tall and dwarf is the descriptive phenotype
• The F1 heterozygote Tt plants have the same phenotype as the TT parent, resulting in dissimilar factors resulting in one being dominant and thus the other being recessive.
• T is dominant for tallness, while t is recessive (dwarfness)

Monohybrid

• Heterozygous plants like Tt are monohybrids, so a cross done between TT and tt is thus a monohybrid cross.
• Recessive traits show in the F2 without blending, we infer traits process from both plants, but during meiosis, alleles separate with only one transmitted to a gamete
• This segregation causes a 50 per cent chance of a gamete containing either allele
• Tall TT plants have gametes with allele T, while dwarf tt plants' gametes have allele t. T from the pollen unites with the egg(t) in fertilization that create hybrids with Tt

Punnett Square developed by Reginald C. Punnett

• Graphical representation calculates probability of offspring genotypes.
• Gametes are written on two sides, and resulting combinations are in the boxes.
• The Punnett Square shows T as pollen from the parental tall (male) and t are the female dwarf. Then the F1 progeny is produced as Tt .
• The monohybrid cross between true-breeding tall and dwarf plants shows phenotypic ratio of tall to dwarf as 3:1, while the genotypic ratio of TT: Tt: tt is 1:2:1.
• Random fertilization results in three kinds of zygotes TT, Tt, or tt.
• One experiment can lead to TT, 1. to Tt and 1. to tt. F1 has a Tt genotype, but the tall phenotype, so from the f2 generation 1. the plants are tall, while the others are Tt which still make it tall. So the T allele makes the ‘tall’ expression
• The character T or 'tall' surpasses other characters due to the dominance of one character over the other, where the f1 generation are tall, f2 plants are 3/4 tall where half is Tt, and 1/4 is TT.
• A phenotypic ratio is 3/4 to 1/4, or a 3:1, but a genotypic ratio is 1:2:1.
• Mendel self-pollinated F₂ plants found that dwarf generates dwarf, so dwarfs are homozygous, which may be observed if you self-pollinate an F₂ plant that is tall.

Test Cross

• To know the F₁ generation is the TT or Tt can be determined by the genotype phenotype ratio.
• Mendel crossed the tall F₂ plant with a dwarf plant, known as a test cross, to determine if the tall plant will carry the recessive trait (Tt) or just dominant (TT)

Law of Dominance

• Characters are controlled by factors.
• Factors occur in pairs.
• In a dissimilar pair of factors, one dominates, and the other remains recessive which is from the expression of each parent.
• F₁ in monohybrid is based on it

Law of Segregation

• This law is based on the fact that alleles do not show any blending, but contain two alleles which segregate during gamete formation so the gamete receives only one trait.
• Homozygous parents make similar gametes, while heterozygous parents produce 2 kinds of equal proportion (50/50)

Incomplete Dominance

• Found that the F1 does not resemble of the 2 parents. inheritance of flower color of the dog flower with RR (true bredding red flowered) with rr which makes F1 to be all pink.
• An explanation of why alleles dominant or recessive, but we must know what a gene can do. 1 gene has 2 copies, or a pair of alleles while in organisms due to changes( modifications of information that particular allele), but this is not the norm.
• Take a gene that has information in creating an enzyme has 2 allelic forms that can be normal and transformation S and a modified to be less efficient or make none at all.

Codominance

• Some F₁ generations show both trait from of the original crossed traits. ABO blood type where I has 3 options of alleles A, B, or i- but humans are dilpoid- where each has has 2 chromosomes
• A and B are all dominant over i. However, where A and B line up, is an ex of Co dominance

Human Blood Groups and Multiple Alleles

• What about multiple alleles? There can exist three governing alleles in blood groups, but only two present themselves, based on environment? In the ABO example.
• Synthesis can effect single produce as with starch in Pea which synthesized through BB and produces large grains. Little synthesis from bb- BB round because dominant allele. However, its based, starch grain determines, so it will show incomplete dominance. But, it doesn’t rely on gene either- so it all relies on phenotype

Inheritance of Two Genes

• Mednl worked and crossed plants that differed, like yellow round vs green shaped, with resulted in the cross had seeds w yellow color and round shape- so which in the pair was dominant?
• A genetic code can be dominant but recessive, lets use Y dominant with recessive being “y”, R dominant with r, So, a cross between
• 2 separate will be identical with YYRR with rryy, uniting and producing F 1 hybrid RrYy- where YY or yy 3. 4 plants had yellow vs ¼ had green, as segregation is 3.1. This segregation is monohybrid

Law of Independent Assortment

• In that cross phenotype, you can wrinkled, yellow; round and green when appearance is 9.1?
• The ratios can have a combination series with 3 yellow and 1 green while round versus wrinkled
• Mednl on these observed that hybrids must contain 2 pairs of alleles on how they independent and unite (permutation +combination- so that is the Law. An Effective square will tell you independent of square meiosis)

Chromosomal Theory of Inheritance

• Why was mendel work ignored until 1900? One the communication wasn’t good at the time- and the that stable distinct genes were unheard of, like why the pair alleles did not like
• “ blend”. It would not explain how continuous relation was observed in nature Mendel’s math approach was new, and he has no provide direct existence or proof of factors" genes"
• De Vries etc rediscovered Mendel’s results due to cell observation of the chromosomes as they move and replicate so the scientists saw that Walther Sudon+ Boveri- used movement explained
• Mendel Laws- recall chromosomes + genes occur in pair alleles are homologs which were observed in paired chromosomes.
• Pairing segregation of chromosomes from chromosomes lead to a pair that Sutton linked +called the chromosomes theory of inheritance( after those ideas Thomas hunt + co lead the base variation of what sexual reproduction produced).
• They crossed many dihybrid with flies to have two genes carried from the same sex link similar with cross of Mendel pea, crossing of parents not independent with results deviating from what should be as dominant.
• Linkage is what coins them- because it is a physical association that doesn’t let the results happen to change.

Polygenic

• They can be more of course than one alleles- the involvement of multiple genes- human skin colors has alleles work in addition the dominance. Can tell lightness of one or the other with which combo and mix exist.

Pleiotropy

• Gene in a phenotype We say an effect gene can’t show phenotypes unless it acts on path that can cause things!
• Ex Phenlketonria. That gene manifest phenotyic as retartation, etc)

Sex Determination

• Early clue can be attributed to insects but heaking that traced through a process sperm receieved it or not which gave it.
• Those lead a lead of investigations through the different mechanics a large insects of the type( X0 type- some is other is not from fertilations.
• However, determine in term which it was named sex chromosomes and others (grasshopper of x0 which male x- whereas XX chromosome. Those leads
• Humans/males/mammales where female males same count- males+female have same autosomal and what the chromosome tells their.

Mutation

• Mutation alters both the DNA and the person. In addition to recreation DNA leads in multiple areas like DNA helix from 5. “to other. Thus gain or lots
• Can cause alter as genes are what control the chromosomal like abnormal cells. These do can rise due change pair.

Mendelian Disorders

• Broad or chromosal ( alter vs mutations vs study patterns like Hemophilia etc)

Color Blidness

• linked of eye so to discriminate and in X and males +female carry it. Carriers can have the son effected despite not caring.

Down sydrome

• Presence of the condition of Trisimy of 21 First Down is how described but the affected has smaller head and tongue out.

Klinefelter is an additional X copy

• Feminish traits

Turner Syndrome

• Caused due absence so femals and fertitlites